The basic properties required of anti-vibration rubbers are strength properties for supporting a heavy body such as an engine, and an anti-vibration performance which absorbs and suppresses vibrations by the supported body. Moreover, when used in a high-temperature environment such as an engine compartment, the anti-vibration rubber, in addition to having, of course, excellent strength properties, a low dynamic-to-static modulus ratio and an excellent anti-vibration performance, is also required to have an excellent heat aging resistance. In addition to the above, because automobiles are used even in high-latitude regions, automotive anti-vibration rubbers are also required to have good low-temperature properties.
Research on compounding given amounts of a rubber component, a crosslinking system and other additives for anti-vibration rubber in order to impart such collectively outstanding properties is actively underway, and numerous patent applications have already been filed. Of these many patent applications, some make deliberate use of bismaleimide compounds to improve the crosslinking system. For example, JP-A 3-258840 discloses rubber compounding art that provides excellent properties, including heat aging resistance and dynamic-to-static modulus ratio, by compounding sulfur, bismaleimide and a specific carbon black with a rubber component.
However, although such rubber compositions do have excellent properties, including heat aging resistance, the dynamic-to-static modulus ratio, compressive set and low-temperature properties do not achieve the desired levels, and so there has existed a need for further improvement.